1. Field of the Invention
The present invention relates to an etching method and a storage medium, and more particularly to an etching method for etching an oxide film using plasma, with a resist film as a mask.
2. Description of the Related Art
To etch a film, such as an SiO2 oxide film, formed to be etched on a wafer for a semiconductor device by plasma according to a predetermined pattern, a substrate processing apparatus makes use of a resist film formed on the oxide film according to the predetermined pattern, as a mask. The resist film has openings for exposing portions of the oxide film at respective locations where via-holes or the like are required to be formed. Plasma enters through the openings to the respective exposed portions of the oxide film to etch the same. It should be noted that the resist film is formed of a photosensitive resin.
In the case of etching the oxide film by plasma generated from a CF-based gas, it is difficult to secure a selection ratio of the oxide film to the resist film due to low resistance of the resist film to the CF-based gas plasma. As a result, in the etching of the oxide film, the resist film can be etched together with the oxide film, which causes deformation of the openings of the resist film. At this time, via-holes formed by the etching are deformed due to the deformation of the openings of the resist film. More specifically, the shapes of the formed via-holes are sometimes not circular in horizontal cross section, and the diameter of the via-holes is sometimes larger than a desired value. In short, it is difficult to obtain a desired etching shape.
To solve this problem, a method of enhancing the resistance of a resist film to plasma has conventionally been developed. For example, a method is known in which a silicon (Si) element is doped into a resist film by a beam prior to etching of an oxide film (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. H03-174724).
However, in the method disclosed in Japanese Laid-Open Patent Publication (Kokai) No. H03-174724, it is required to dope the silicon element into a resist film by a beam, which makes it necessary to add a special device such as a beam irradiation device to a substrate processing apparatus or provide the special device separately from the substrate processing apparatus. Therefore, the improvement of the strength of a resist film cannot be attained easily and conveniently, which makes it difficult to obtain a desired etching shape.